Implantable electronic medical devices such as cardiac pacemakers are often powered by fully integrated power supplies which are implanted with the electronics as a single unit. When such pacemakers are implanted, there is no convenient way of testing the power supply condition to determine its present vitality or state of depletion. Because the life of the patient often depends on the proper operation of the pacemaker, which in turn is dependent on the power supply condition, it is imperative that some means of accurately determining end of power supply life be available to the patient and/or physician.
Power supply life, and the need for replacement, have been predicted on a statistically determined schedule. However, some units will fall short of the statistically determined life even with the introduction of a carefully determined safety factor. It is also considered better not to disturb or remove an implanted pacemaker which is operating properly unless absolutely necessary. Even though the surgery required for removal of an implanted pacemaker is relatively minor, the danger of complicat ons or accident is always present, and it is better avoided.
Means to indicate to a patient that the pacemaker power supply is depleted are known in the prior art, and have involved circuitry for sensing an indication of power supply depletion and linearly changing the pacemaker generator output frequency rate to a different, usually lower, frequency rate as from 70 to 65 beats per minute. This change can then be detected by a patient when taking his pulse. Many patients, however, may not be in the habit of regularly taking their pulse. Such a patient's pacemaker power supply could become dangerously depleted before he would detect that the pacemaker is operating improperly due to inadequate power. An underpowered pacer could result in serious complications, or even death.